Boolean

A Boolean stores a value indicating True or False. It can be used as an expression in an If-statement. It can also store the result of an expression.

Booleans are used throughout VB.NET programs. We can return a Boolean from a function, or pass a Boolean as an argument.

First Boolean example

We assign a Boolean variable to True or False. Then we use Booleans in a variety of ways in this simple program.

Module Module1
    Sub Main()
        Dim value As Boolean = True
        Console.WriteLine(value)

        ' Part 1: flip the boolean.
        value = Not value
        Console.WriteLine(value)

        ' Part 2: this if-statement evaluates to false.
        If (value) Then
            Console.WriteLine("A")
        End If

        ' Part 3: evaluates to true.
        If (Not value) Then
            Console.WriteLine("B")
        End If

        ' Part 4: store expression result.
        Dim result As Boolean = Not value And 1 = Integer.Parse("1")
        Console.WriteLine(result)
    End Sub
End Module
True
False
B
True

Return Boolean

A Function can return True or False. We can even return the result of an expression that evaluates to True or False. Here in IsEmpty we return an expression's result.

Module Module1

    Dim _values As List(Of String) = New List(Of String)

    Function IsEmpty() As Boolean
        ' Return a boolean value.
        ' ... This returns true if the Count is equal to 0.
        ' ... It returns false otherwise.
        Return _values.Count = 0
    End Function

    Sub Main()
        ' Use the IsEmpty boolean method.
        Console.WriteLine(IsEmpty())

        ' Add an element to the List and call IsEmpty again.
        _values.Add("bird")
        Console.WriteLine(IsEmpty())
    End Sub

End Module
True
False

We examined the Boolean type in VB.NET. With Boolean, you can store True and False and also the result of expressions that evaluate to True or False.

Notes, continued

Booleans are necessary for If and ElseIf statements, and careful use of them can make your programs clearer and faster.